The present disclosure relates generally to controlled motion systems and, more specifically, to controlled motion systems having more than one linear motor section and a technique of joining the linear motor sections together using a magnetic flux bridge such that the likelihood of interruption or a change in the level of magnetic flux between the linear drive sections is reduced.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
There are many processes that benefit from providing the controlled motion of one object relative to another. For example, assembly lines have been used for well over 100 years to facilitate rapid and efficient production. In a typical assembly line, an article being manufactured moves from one station to another, typically via a conveyor belt or by some other motorized means. As the semi-finished article moves from one work station to another, parts are added or processes are performed until the final product is completed. In addition to this type of assembly automation, controlled motion systems may also be used for packaging, transporting objects, machining, etc. Conveyor belts typically use an endless belt that is stretched between a motor and one or more idlers, which results in a relatively high number of moving parts and associated mechanical complexity. Moreover, each item on a conveyor belt necessarily moves at the same speed and in the same spaced apart relationship relative to other items on the conveyor belt. Similarly, ball screws and many other types of linear motion systems also rely upon rotary motors to produce linear motion, and they suffer from similar problems.
The application of controlled electromagnetic motion systems to a wide variety of processes, such as those mentioned above, provides the advantage of increasing both the speed and flexibility of the process. Such controlled motion systems may use linear motors that employ a moving magnetic field to move one or more elements along a path. The movable element is sometimes known as a carriage, pallet, tray, or mover, but all such movable elements will be referred to here collectively as a “mover.” Such linear motors reduce or eliminate the need for gear heads, shafts, keys, sprockets, chains and belts often used with traditional rotary motors. This reduction of mechanical complexity may provide both reduced cost and increased speed capability by virtue of reducing inertia, compliance, damping, friction and wear normally associated with more conventional motor systems. Further, these types of controlled motion systems may also provide greater flexibility than rotary motor systems by allowing each individual mover to be independently controlled along its entire path.
Electromagnetic controlled motion systems typically use interconnected track sections, where each section has a plurality of individually controlled coils that provide independent control of one or more movers that travel along the track. Such systems include a positioning system that often employs a plurality of linear encoders spaced at fixed positions along the track and linear encoder strips mounted on each mover to sense their position. Such linear encoders are typically “incremental absolute” position encoders that are coupled to a controller or counter, and that operate by sensing and counting incremental pulses (or that digitize sine/cosine signals to create these pulses) to count up or down after a mover has traveled past a reference point. These incremental encoders, however, can provide an absolute position signal only after performing a homing and commutation alignment procedure for each mover at power up. This requires moving each mover a certain distance along the track to find the zero reference position and the magnetic pole positions.
Presently, such controlled motion systems utilizing electromagnetic linear motors suffer from a particular deficiency. Specifically, tracks are generally assembled by combining individual track sections, such that each section is adhered or connected to an adjacent section along their contact surfaces, such as by use of an epoxy or other such material, and then covered or encased in stainless steel or similar material. During actual use of the system, a mover travels along the track from section to section through employment of a magnetic field created by the individually controlled coils positioned along each section of the track. Often, in the region where the mover leaves one section of the track and reaches the next section, there is typically a disturbance or weakening in the magnetic field that results in a relatively large increase in resistance (often referred to as cogging) as compared to the magnetic field in the middle of a section. This disruption or weakening in the magnetic field is the result of an air gap along the contact surfaces of the assembled track sections generally caused by non-precise milling of the adjacent track sections so exposed cores do not magnetically touch, or the result of the epoxy or other non-magnetic covering creating a substantially non-magnetic gap between the individual track sections. This disruption or weakening in the magnetic field between adjacent track sections is problematic in that it often leads to lost performance, noise, or false readings along the track. Further, when a mover experiences a disruption or weakening in the magnetic field during operation of the motion control system, the counting process by the controller or counter is often lost or the pulse counting is disrupted. This requires the movers to be driven back to a reference point or home position to initialize or reset the counting process. This initialization or resetting of the counting process may result in loss of production time.
Accordingly, what is needed is a controlled motion system having one or more linear motors positioned along a track formed from two or more sections such that the likelihood of interruption or the level of disturbance or weakening in the magnetic field along and between adjacent linear motor sections is reduced or minimized.